I really don't remember doing any in-depth reading on the background of the design decision on Gemini, but it does seem a curious decision.

Ejection seats would be no good at transonic speeds (the pilots would be killed by wind blast if not friction heating), so there would be a fairly significant segment of the flight during which there would effectively have been no functional escape system.

The Gemini-Titan had pretty serious takeoff acceleration. I am pretty sure it was pushing Mach 1 within 20-30 seconds of liftoff.

I suspect the bottom line reasoning was an escape tower system sufficient to pull the Gemini capsule free would have been fairly sizable and maybe push the total spacecraft weight over the Titan II's orbital launch capacity. As I recall it also had to do with the originally planned paraglider landing system.

If anyone else is more completely informed on the whole design discussion/debate on Gemini on the launch escape mechanism, I would certainly love to hear more about it. I would guess there were some fairly heated/pointed discussions of the matter when the astronauts were brought into the conversation.

I was looking at and comparing the different earlier manned Space Flight vehicles of the U.S. and I was wondering why the Gemini Titan looked like a departure from the others and then it hit me.

It doesn't have an escape tower.

So then my next question is why? I'm sure someone here knows.

An example of what I'm talking about is attached.

David

Gemini was equipped with ejection seats... thus no need for a tower...

The Atlas was powered by LOX and kerosene... and Redstone was powered by LOX and alcohol... the later Saturn was powered by LOX/kerosene and LOX/LH2 (enough to make a small atom bomb yield if it blew up). The Titan II, on the other hand, was powered by nitrogen tetroxide oxidizer and Aerozine 50 (50/50 mix of hydrazine and unsymmetrical dimethyl hydrazine). These propellants are room temperature storables, and also will ignite on contact with each other (hypergolic). They won't explode when mixed, just burn at a predictable rate, unlike LOX and other propellants which burn EXTREMELY FAST in an uncontrolled fireball if the vehicle were to fail. Thus, due to the slower, more predictable burn rate between NTO and UDMH/hydrazine, if the Titan rocket failed on the pad or early in flight, it was felt ejection seats were sufficient to ensure the astronauts survival should they need to escape a failing booster. The Gemini spacecraft, since one of the requirements was to be able to conduct spacewalks, also was equipped with large individual hatches for each astronaut directly "overhead" for each astronaut. These hatches would be jettisoned shortly before the ejection seats fired to blast them out of the capsule in an ejection. The Mercury spacecraft, on the other hand, was equipped only with a small, off-center hatch that one could barely squeeze through, and there simply was no way they could make an ejection seat work with it, nor was their enough weight allowance in the design to permit the use of a heavy ejection seat. Besides, an ejection seat was not sufficiently powerful to get an astronaut safely away from an exploding Atlas, and might not have been for a Redstone, either... hence the launch escape tower on Mercury.

By the time the Apollo came along, weight was a MUCH more important consideration in the design than it had been on Gemini, due to the requirements of sending extra weight to the Moon and back. Plus, there simply wasn't room in the spacecraft for THREE heavy ejection seats, and of course requiring three heavy hatches instead of one would also greatly complicate spacecraft design and compromise the mission. Plus, the Apollo was designed to fly on Saturn V (and Saturn IB) and both of those launch vehicles were SO large and would create fireballs SO huge if they failed on the pad or early in flight, that ejection seats would not be powerful enough to get the astronauts safely out of the fireball... hence the return to a launch escape tower for Apollo.

In fact, the Apollo escape tower was more powerful than the Redstone that launched Alan Shepard and Gus Grissom on the first two Mercury missions back in 1961...

Later! OL JR

__________________
The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!

I believe that the ejection seats were for a low-level, low-speed abort. At a certain part of the envelope they would use the four retro rockets as abort motors to initiate a safe abort.

Chas

Yes... the ejection seats were "usable" on the pad up until about 30-40 seconds into the flight IIRC... (I was just reading Mike Collins' account of his Gemini flight and he made a passing reference to it, but it's been a couple days ago and we've had a lot going on). After that, the solid retrorockets would have been used for escape, or simply "ride it out" until the capsule slowed down enough after the Titan disintegrated to subsequently eject...

The ejection seats were a pretty dicey proposition anyway... a lot of the astronauts described the ejection seat system the same way that John Young described proposals for STS-1, the first flight of the shuttle, to simulate a "Return To Launch Site" type abort in flight rather than flying into orbit... "It was taking a high risk of death to avoid certain death"... Hence the plans to demonstrate RTLS on an actual shuttle flight were shot down fairly quickly. Remember that the first four shuttle missions (IIRC) were equipped with ejection seats as well... but they were pulled out when they added seats for seven crew-- there was no way to eject from the mid-deck, and so it wouldn't be fair for the four folks sitting "upstairs" to have ejection seats while the other three "down below" would just have to ride what was left of the shuttle all the way in if there was an emergency. John Young didn't have much faith in the ejection seats on shuttle either IIRC...

That was the mindset of the astronauts and a big part of the reason why Wally Schirra and Tom Stafford didn't punch out of Gemini 6 when it ignited, the clock started (which was supposed to be triggered by the vehicle physically lifting off the pad, which pulled a plug out of the aft body of the Titan II, triggering the spacecraft clock to start counting... the shutdown of the Titan engines was triggered by this plug popping out too soon-- the safety system determined that the thrust was insufficient because the plug popped out during engine start and thrust buildup, and so the controller shut the engines down before liftoff. The procedure that the astronauts had been trained for was to eject in the event of a failed startup/liftoff, so technically speaking, according to the rulebook, they SHOULD have ejected on the pad... BUT, of course it would have destroyed the spacecraft and any chance of there even being a Gemini 6 (6A as it turned out). Wally was convinced that his odds were better staying in the capsule than ejecting, because absolutely EVERYTHING had to come off right, and you had to have luck on your side, to survive a Gemini ejection... If the doors didn't blow correctly or the timing was off, you'd have your head in your lap. If the ejection seats didn't burn right and fly the correct trajectory, you'd arc straight into the ground backwards and head first at high velocity. Even if the ejection seats followed the correct trajectory and arced upwards and then burned out and released the chute, it was still a very low altitude chute deployment and thus extremely risky... CCWilliams had been killed trying to eject from his crippled T-38 after its controls locked up and it went inverted, and Ted Freeman had been killed ejecting from his T-38 after it was hit by a goose and flamed out on approach to Ellington Field in Houston (the wiki article says he didn't eject, but that's not what Deke Slayton told in his account of the accident, as he was one of the first on the scene-- Ted had ejected, but too low and his parachute didn't have time to inflate and slow down before he hit the ground. Thus the decision that Wally and Tom made to "sit it out" in the Gemini rather than risk death in an ejection... a decision that saved the mission, as it turned out, and perhaps saved their lives had the ejection not gone well...

Interestingly enough, it was lucky that the plug dropped out prematurely, and that the engines shut down... during the inspection of the rocket in preparation for another launch attempt a few days later, it was discovered that a plastic cover had been left in place inside a propellant line feeding one of the first stage engines. Had the rocket lifted off normally, the cover would have compromised the propellant flow into the engine, and the resulting lack of power would have REQUIRED an abort and the destruction of the booster shortly after it lifted off, since it would have insufficient power to continue flying. Thus, the plug popping out, and Wally's cool calculation not to abort, allowed the re-inspection of the booster that found the cover left in the propellant line, and allowed the rocket to be repaired and the countdown reset for Gemini 6A's successful first rendezvous in space with Gemini 7 a few days later...

Kinda funny how those things work out sometimes...

Later! OL JR

__________________
The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!

There was a rocket sled test of the Gemini ejection systems done at Edwards, I believe.
One test had the sequencing off a ..... bit.... The mannequins(crash test dummies) came plowing THROUGH the closed hatches .(,my keyboard sticks on the exclamation sign).
I'd really like to find footage of this. There has to be some out there on the Interlink.
FWIW most ejection seats are able to punch through a canopy if it doesn't jettison. There are canopy breakers mounted just above the headrests. Having worked on them in the USAF. I can tell you that an ejection is no picnic. But, it does give you a chance to survive.
Mark T

There was a rocket sled test of the Gemini ejection systems done at Edwards, I believe.
One test had the sequencing off a ..... bit.... The mannequins(crash test dummies) came plowing THROUGH the closed hatches .(,my keyboard sticks on the exclamation sign).
I'd really like to find footage of this. There has to be some out there on the Interlink.
FWIW most ejection seats are able to punch through a canopy if it doesn't jettison. There are canopy breakers mounted just above the headrests. Having worked on them in the USAF. I can tell you that an ejection is no picnic. But, it does give you a chance to survive.
Mark T

Yes, I recall comments about this test in one of the astro's autobiographies......several of the astronauts were on hand to witness the test and they were NOT impressed to say the least. As mentioned by others above, I don't think any of them would have tried to use the ejection seats unless there were ABSOLUTELY no alternative. I seem to recall a comment from Deke that, in hindsight, the ejection seats were a dumb choice over an escape tower.

There was a rocket sled test of the Gemini ejection systems done at Edwards, I believe.
One test had the sequencing off a ..... bit.... The mannequins(crash test dummies) came plowing THROUGH the closed hatches .(,my keyboard sticks on the exclamation sign).
I'd really like to find footage of this. There has to be some out there on the Interlink.
FWIW most ejection seats are able to punch through a canopy if it doesn't jettison. There are canopy breakers mounted just above the headrests. Having worked on them in the USAF. I can tell you that an ejection is no picnic. But, it does give you a chance to survive.
Mark T

Yeah, but aren't they usually punching through PLEXIGLASS rather than a aluminum, steel, titanium, and Rene 41 metallic shingles like on the hatches of Gemini??

The best way I've heard ejecting from an aircraft was summed up by "it's better than the alternative"...

Later! OL JR

__________________
The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!